This paper explores the viability of the bonded crack retarder concept as a device for life extension of damage tolerant aircraft structures. Fatigue crack growth behaviour in metallic substrates with bonded straps has been determined. SENT and M(T) test coupons and large scale skin-stringer panels were tested at constant and variable amplitude loads. The strap materials were glass fibre polymer composites, GLARE, AA7085 and Ti-6Al-4V. Comprehensive measurements were made of residual stress fields in coupons and panels. A finite element model to predict retardation effects was developed. Compared to the test result, predicted crack growth life had an error range of -29% to 61%. Mechanisms and failure modes in the bonded strap reinforced structures have been identified. The strap locally reduces substrate stresses and bridges the crack faces, inhibiting crack opening and reducing crack growth rates. In the absence of residual stress, global stiffness ratio accounts for effects of both strap modulus and strap cross section area. In elevated temperature cure adhesives, retardation performance was best in aluminium and GLARE strap materials, which have the closest thermal expansion coefficient to the substrate. Strap materials of high stiffness and dissimilar thermal expansion coefficient such as titanium had poor retardation characteristics.

a b s t r a c tFibre-Metal Laminates (FML) such as GLARE are of interest as bonded crack retarders (BCR) to improve the fatigue performance of aircraft structures. The degradation of the performance of the crack retarder in service if subjected to damage is a critical factor in designing with this concept. Bonded assemblies of an aluminium alloy substrate reinforced with a GLARE strap were prepared, and were subjected to low velocity impact damage onto the GLARE, with impact energies ranging from 10 to 60 J. The thermal residual stresses developed during the bonding process of the GLARE to the aluminium were determined using neutron diffraction, and the change in the thermal residual stresses owing to impact damage onto the GLARE was evaluated. Pre-and post-impact fatigue performance of the BCR assemblies has been investigated. The results show that the BCR provides an improvement in fatigue life, but the reduction is impaired following impact damage. The results show that monitoring of impact damage will be critical in the damage tolerance assurance for aerospace structures containing bonded crack retarders.

This study explored youths’ perceptions of the nature and dilemmas of being a bystander in cyberbullying. Although there are many benefits of peer interactions through social media, there are risks, including cyberbullying. Bystanders are integral in the dynamics and harm in both face-to-face and cyberbullying. Using a qualitative approach, authors share youth voices on the experience of witnessing cyberbullying and the dilemmas they face in deciding whether and how to respond to support a peer. Authors conducted thematic analysis of qualitative interviews with 16 adolescents. Youths described a range of feelings experienced by witnesses, from discomfort and anger to moral disengagement and justification for cyberbullying. Youths reported three forms of bystander roles: outsider, assistant, and defender, consistent with traditional bullying. The dilemmas they faced in witnessing and intervening that emerged were consistent with the five stages of bystander decision making. Youths indicated that the solutions for cyberbullying rest on the shoulders of adults.

Purpose -This paper aims to present the implementation of a finite element (FE) model used to establish crack and delamination development in a Glare reinforced aluminium plate under fatigue loading. This model predicts the behaviour of bonded GLARE straps used as crack retarders for life extension of aircraft structures. In particular, it takes into account the interaction that exists between the substrate crack and the delamination crack at the interface with the reinforcement. Design/methodology/approach -In this work, a 3D FE model with three-layer continuum shell elements has been developed to calculate changes in substrate stress intensity and in fatigue crack growth (FCG) rate produced by bonded strap reinforcement. Both circular and elliptical strap delamination geometries were incorporated into the model. Calculated stress intensity factors (SIFs) were used together with measured FCG data for substrate material to predict FCG rates for the strapped condition. Findings -The model predicted a decrease in the SIF and a retardation of FCG rates. The SIF was predicted to vary through the thickness of the substrate due to the phenomenon of secondary bending and also the bridging effect caused by the presence of the strap. The influence of delamination shape and size on substrate crack stress intensity and delamination strain energy release rate has been calculated. Originality/value -This research aims at developing modelling techniques that could be used when studying larger reinforced structures found in aircraft.

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